This invention is concerned with the treatment of engine coolants in the cooling systems of automotive vehicles; more especially the invention is concerned with a filter device for the coolant which provides controlled release of corrosion inhibitor into the coolant.
Engine coolants in an automotive vehicle are continuously circulated during operation of the vehicle to remove heat developed by the engine. Corrosion inhibitors are added to the coolant to prevent corrosion of parts of the cooling system. It is preferable to filter the flowing coolant to remove foreign matter and debris entrained therein which may damage, block or otherwise interfere with the cooling system.
A typical engine coolant is based on an antifreeze mixture of ethylene glycol, diethylene glycol and water. Corrosion of the metal parts contacted by the coolant occurs if the mixture is not maintained with approximately a 50% content of correctly inhibited ethylene glycol. Thus corrosion inhibitors are added to coolants, typically a mixture of one or more salts, for example, phosphates, borates, nitrates, nitrites, silicates, arsenates, molybdates or benzoates; and one or more organic compounds, for example, benzotriazole, tolyltriazole or mercaptobenzothiazole, to prevent corrosion of metal parts contacted by the coolant.
It is necessary to add additional corrosion inhibitor to the coolant periodically in order to maintain a desired level of corrosion protection: Corrodible containers for automatically dispersing corrosion inhibitor to the coolant have been proposed, for example in U.S. Pat. Nos. 4,333,516, 4,338,997 and 4,347,895.
Filters are employed in cooling systems to filter the flowing coolant, thereby removing foreign matter and debris. Foreign matter in the form of particles suspended or entrained in the coolant may absorb corrosion inhibitor thereby reducing the available content of corrosion inhibitor in the coolant, may produce erosion damage, and may affect seal integrity. Thus filters also function to prevent reduction of corrosion inhibitor content.
Pellets of corrosion inhibitors have been incorporated in filter devices, however, these have a short life and the filter devices are usually replaced at recommended intervals of 12,000 to 20,000 miles when the corrosion inhibitor pellet supply originally in the device is depleted, even though the filter medium itself has an effective life of 60,000 miles or more.